test: move @let test out of known_bugs

@let parses correctly now (fix landed in 083e394). Moving the test into
control_flow.txt alongside the other @-construct tests and removing the
now-empty known_bugs.txt.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

test/corpus/control_flow.txt

@@ -148,3 +148,28 @@
                   (attribute_or_control
                     (html_attribute
                       (attribute_name))))))))))))
+==================
+@let statement
+==================
+
+@fn calc() { @let n = 42; }
+
+---
+
+(template
+  (template_element
+    (function_definition
+      (identifier)
+      (parameter_list)
+      (content_block
+        (template_node
+          (template_control_flow
+            (let_statement
+              (simple_pattern
+                (identifier_pattern
+                  (identifier)))
+              (expression
+                (primary_expression
+                  (literal
+                    (number_literal
+                      (integer_literal))))))))))))

test/corpus/known_bugs.txt

@@ -1,25 +0,0 @@
-==================
-@let statement
-==================
-
-@fn calc() { @let n = 42; }
-
----
-
-(template
-  (template_element
-    (function_definition
-      (identifier)
-      (parameter_list)
-      (content_block
-        (template_node
-          (template_control_flow
-            (let_statement
-              (simple_pattern
-                (identifier_pattern
-                  (identifier)))
-              (expression
-                (primary_expression
-                  (literal
-                    (number_literal
-                      (integer_literal))))))))))))